Parents concerned about their daughters putting on extra pounds may have a new reason to worry. Overweight girls are more likely to start having sex early, to have multiple partners during their teen years, and to eschew condoms compared to thinner teens, a new study shows. And the situation worsens as the number of excess pounds goes up.

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South Carolina researchers found that obese girls were almost three times as likely as others to have had sex before age 13 and 30 percent more likely to have had sex with more than three partners during their teen years, according to the study presented this month at the annual meeting of the American Congress of Obstetricians and Gynecologists.

Girls who were simply overweight had a lower, but still significant, risk of starting sex early. Compared to normal weight teens, they were 60 percent more likely to begin sex before age 13 and 30 percent were likely to have had sex with more than three partners.

The study found that 6 percent of normal weight teens had sex before age 13, as compared with 11 percent of overweight teens and 15 percent of obese teens. And 39 percent of normal weight teens reported having sex with more than three partners as compared with 45 percent of overweight teens and 47 percent of obese teens.

Making matters worse, obese and overweight girls were also less likely to use condoms and other birth control. The study found that girls with weight issues were almost 20 percent less likely use condoms than thinner girls, and more than 30 percent less likely to use other methods of contraception.

The magnitude of the findings surprised even the researchers, said Dr. Margaret Villers, the study’s lead author. “We didn’t realize what a strong predictor body weight would be,” added Villers, an assistant professor at the Medical University of South Carolina.

Villers and her colleagues analyzed data from 21,773 teenage girls who had taken part in the Centers for Disease Control and Prevention’s Youth Risk Behavior Survey. The survey is given to students at a broad range of middle schools and high schools across the nation every other year.

Overweight girls tend to hit puberty earlier
One possible explanation for the findings may be the impact excess pounds have on girls’ bodies. Overweight and obese girls tend to hit puberty earlier than those of normal weight.

“They develop sooner,” Villers explained. “They look like women sooner. And maybe that’s why they are more likely to be pressured by their boyfriends to have sex at a younger age.”

Another factor could be low self-esteem and poor body image, which have been correlated with obesity in other studies.

“It may be harder for girls who don’t feel good about themselves to say ‘no,’ or even to stop a partner long enough to say they need to use a condom,” Villers said.

She said she decided to look at the relationship between weight and sexual activity in teens because of the high rate of obesity in South Carolina, where she practices, and the exploding rate of sexually transmitted diseases in her area. She had noticed in her own practice that overweight girls seemed to start having sex earlier.

Villers said the rate of pregnancy and STDs in heavy girls haven't been studied yet.

Low self-esteemShe says she isn’t sure how to stop heavy girls from having sex early, but suspects that efforts to build self-esteem might help. Further, she said, young women need to be taught how to stand up for themselves. “It’s hard to say ‘no,’ if you feel badly about yourself and someone is validating you, saying ‘you’re attractive, and I want to have sex with you,’” she said.

Parents can play a big role in helping their daughters not only to eat right, but also to develop the social skills needed to ward off sexual advances, said Patrick Tolan, a professor in the department of psychiatry and neurobehavioral sciences at the University of Virginia and director of Youth-Nex: The University of Virginia Center to Promote Effective Youth Development.

But, Tolan allowed, it can be a tough line for parents to straddle. As they try to encourage weight loss through healthy diet and exercise, parents also need to be protecting their daughters’ self image, Tolan said.

Because of society’s emphasis on thinness, overweight girls may feel so unattractive that they start having sex as a way to hang on to a partner. “Parents need to find a way to help their daughters feel good about themselves,” he said.

Though the results are convincing, parents shouldn’t overreact, said Dr. Lauren Chernick, a researcher in pediatric medicine at Columbia University Medical Center.

“It’s not as though every overweight girl is having sex just because she’s overweight,” Chernick added. “And, of course, the flip side of that is that parents shouldn’t assume that they don’t have to worry if their daughters are normal weight.”

What researchers do know is that girls who start having sex early and with many different partners are more likely to become pregnant, Chernick said.

“The conversations parents have with a daughter should be the same whether or not the girl is overweight,” she added. “Parents need to talk about sex and about how girls can protect themselves from sexually transmitted diseases and pregnancy.”